Variable temperature seal element

ABSTRACT

Devices and methods for fusing materials using a heating element, where the overall mass to be sealed varies along the length of the seal. According to the invention, the heating element has a different profile in different areas. According to some aspects, the thickness and/or cross section of the heating element is different in different areas so that when a current is passed through the heating element, each area heats to a different degree. In some aspects, the heating element is shaped to conform to the shape of the parts to be fused together. The transition between areas of different thickness or cross-sectional area, or between areas of different shape may be sharply defined. This abrupt transition may be created by machining the heating element to a finished shape rather than bending flat stock to shape.

FIELD OF THE INVENTION

The subject invention relates to systems and methods for heat sealing.More particularly, the subject invention relates a sealing element withan engineered profile to allow for targeted areas of differenttemperature to be contemporaneously created on the same element duringthe sealing process.

BACKGROUND OF THE INVENTION

A heat sealer is a machine used to seal products and packaging byjoining materials using heat. The basic concept is to join twothermoplastic components by applying heat and pressure until thematerials melt and flow together, then allowing the components to cool.

There are several different types of heat sealing devices. Oneparticular class of devices, called impulse heat sealers, operates byholding the materials to be joined between jaws that contain one or moreresistive heating elements. The materials are held in place by pressure,and heat is applied to the materials by applying an electric current tothe heating elements until the materials reach a desired temperature.The heat is maintained until enough time has passed for the materials toflow together adequately. The materials are then allowed to cool,sometimes with the aid of a cooling mechanism, which allows thematerials to fuse together.

The strength and quality of the seal that is formed is largely a resultof using properly designed components with appropriate materials, andapplying correct amounts of temperature and pressure for an appropriateamount of time.

A typical heat sealing application involves fusing two thermoplasticsheets or films to create a bag. In the simplest bags, the sheets areuniform monolayers, and a heat sealer is used to create fused edgeseals.

In an application where flat films are fused, the resistive heatingelements used in the heat sealer are usually straight pieces of drawnwire or ribbon that are made from a suitable material such as nichrome.The uniform cross-sectional area of such heating elements results in auniform temperature along the element. This is due to the uniformcurrent density that arises in the uniform resistive element at steadystate when current is passed through the element. Such elements functionwell in simple applications because the materials to be sealed are of auniform material and thickness.

It is sometimes desirable to seal more complex arrangements ofmaterials. One such application is to seal an object or objects betweentwo sheets such that the sheets form a bag, and such that the object orobjects protrude out of the bag through the seal. In these more complexapplications, the sheets may be sealed together in places, and sealed tothe objects in other places. An example of such a complex application isshown in FIG. 1, where tubes are sealed between two poly sheets to forma medical IV bag with two ports. However this added complexity ofconstruction has a number of implications for creating the seal.

One problem that arises is that unlike the simple case of sealing twoflat films, the materials to be sealed are not uniform in mass,thickness, and/or melting or heat-sinking properties. This means thatthe heating requirements to form a proper seal are different along thelength of the seal. For example, in FIG. 1, the portions of the sealwhich fuse only the two films will require less heat energy to form theseal than the portions which fuse the tubes between the films. This isbecause the mass of the tubes requires more heat to melt, and also actsas a heat sink, drawing heat away from the films.

Because of these effects, a standard heating element having a uniformcross-sectional area may yield undesirable results when sealing complexarrangements of components. This is because in order to use a standardheating element to form the seal, either the temperature, the time theheat is applied, or both must be increased in order to ensure that aseal is formed in the areas of increased mass.

However, none of these solutions is desirable from a productionstandpoint. By increasing the heating time, production is slowed andenergy costs increase. Further, increased heating time alone may not beadequate in certain circumstances where higher mass parts dissipate heatinto the environment rapidly. By increasing the temperature of theelement, production speed may be maintained, but the temperaturerequired to seal areas of greater mass may be too great for thinnerthermoplastic components. This can result in deformation of the finishedproduct, unreliable seals, degradation of materials, and so forth. Theexcess heat applied to the thinner regions in order to adequately heatthe thicker regions also represents increased energy that is wasted.

Another problem in such applications arises due to the complex shape ofthe seal. In order to properly apply heat to the surfaces to be joined,the heating element must be shaped to follow the contours of the desiredseal, which includes the parts that protrude through the seal.Typically, this is done by simply bending the wire or ribbon ofresistive material into the proper shape. However, bending the elementin this way can yield inadequate results.

One issue arises if the bending process is not adequate to create asharp transition between sections of the element having differentshapes. This may prevent the heating element from making proper contactwith the components to be sealed in the “corners” between profileshapes, thus negatively affecting the bond.

Another issue arises if the bending process at a sharp corner strainsthe material locally, resulting in a thinning or distortion of theheating element at that point. This may result in an increase intemperature at the corners between shapes due to locally increasedcurrent density, which may negatively affect the bond or damage thematerials.

Many other complex arrangements of materials are possible, all of whichimplicate the issues identified above. For example, it may be desirableto seal an article having multiple layers, having gussets in discreteareas, having areas of dissimilar materials, or having fitments or tabs(such a s a hang tag) sealed into the article. It may also be desirableto apply a “cut/seal”, where an area of the sealer cuts through thematerials using added heat and/or pressure.

What is desired, therefore, is a single resistive heat sealing elementwhich possesses the true shape desired, and which also allows for atargeted temperature profile to be created therealong (i.e., highertemperatures in areas of film-to-tube sealing and lower temperatures inareas of film-to-film sealing).

SUMMARY OF THE INVENTION

The inventive concepts described above can be readily adapted for anynumber of other similar applications. For example, the inventive sealingelement can also be used in applications where solid elements (such as,for example, rows of slats, rods, bars, or the like) instead of or inaddition to hollow tubes and/or port fitments or the like are to besealed between layers of film.

Accordingly, it is an object of the present invention to provide asingle resistive heat sealing element having an engineered profile. Itis a further object of the present invention to provide a resistive heatsealing element.

These and other objectives are achieved by providing a heat sealer forfusing components; having a heating element; an electrical power sourceconnected to the heating element; and, a holder configured to positionthe components with respect to the heating element; wherein: the heatingelement comprising a resistive material having a first end and a secondend; a first portion of the heating element exhibiting a firstelectrical resistance; a second portion of the heating elementexhibiting a second electrical resistance that is different from thefirst electrical resistance; and, wherein when electrical current ispassed through the heating element, the first portion and the secondportion generate different heat levels

In some embodiments, an amount of heat transferred to the componentsfrom the first portion is greater than an amount of heat transferred tothe components from the second portion.

In some embodiments, the first portion and the second portion are joinedat a transition such that the first resistance transitions to the secondresistance at the transition.

In some embodiments, the first portion has a first cross-sectional area;and, the second portion has a second cross-sectional area that isgreater than the first cross-sectional area. Optionally, thecross-sectional area of at least one of the first portion or the secondportion varies along its length. Optionally, a cross-sectional area ofthe heating element transitions immediately from the firstcross-sectional area to the second cross-sectional area at thetransition.

In some embodiments, the first portion and the second portion have anequal width; the first portion has a first thickness; and, the secondportion has a second thickness that is greater than the first thickness.

In some embodiments, the first portion has a first curvature and thesecond portion has a second curvature that is different than the firstcurvature.

In some embodiments, the first curvature transitions to the secondcurvature at the transition.

In some embodiments, the first portion is curved and the second portionis straight.

In some embodiments, the resistive material conforms to the shape of thecomponents.

In some embodiments, the first portion conforms to a first shape of atleast one of the components and the second portion conforms to a shapethat is different from the first shape. Optionally, the ratio of thefirst thickness to the second thickness is 0.012:0.015. Optionally, thewidth is 0.25 inches, the first thickness is 0.012 inches, and thesecond thickness is 0.015 inches.

In some embodiments, the heating element is made from a homogeneousresistive material.

Other objectives are achieved by providing a heating element for use ina heat sealing device, comprising a first end and a second end; whereina first portion of the heating element has a first electricalcharacteristic; a second portion of the heating element has a secondelectrical characteristic that is different from the first electricalcharacteristic; and, the first portion and the second portion are joinedat a transition such that the first electrical characteristictransitions to the second electrical characteristic at the transition.

In some embodiments, the electrical characteristic is resistance.

In some embodiments, the first portion has a first cross-sectional area;and, the second portion has a second cross-sectional area that isgreater than the first cross-sectional area.

In some embodiments, a cross-sectional area of the heating elementtransitions from the first cross-sectional area to the secondcross-sectional area at the transition.

In some embodiments, the cross-sectional area of at least one of thefirst portion or the second portion varies along its length.

In some embodiments, the first portion and the second portion have anequal width; the first portion has a first thickness; and, the secondportion has a second thickness that is greater than the first thickness.

In some embodiments, the first portion has a first curvature and thesecond portion has a second curvature that is different than the firstcurvature. Optionally, the first curvature transitions to the secondcurvature at the transition.

In some embodiments, the first portion is curved and the second portionis straight.

In some embodiments, the resistive material is configured to conform tothe shape of the components.

In some embodiments, the first portion conforms to a first shape of atleast one of the components and the second portion conforms to a shapethat is different from the first shape. Optionally, the ratio of thefirst thickness to the second thickness is 0.012:0.015. Optionally, thewidth is 0.25 inches, the first thickness is 0.012 inches, and thesecond thickness is 0.015 inches.

In some embodiments, the resistive material is homogeneous.

Other objectives are achieved by providing a method of manufacturing aheat sealing device, comprising the steps of: providing a heatingelement; providing an electrical power source connected to the heatingelement; and, providing a holder configured to position the componentswith respect to the heating element; wherein the heating element has afirst end and a second end and comprises a resistive material; a firstportion of the heating element exhibits a first electrical resistance; asecond portion of the heating element exhibits a second electricalresistance; and, wherein when electrical current from the electricalpower source is passed through the heating element, the first portionand the second portion generate different heat levels.

In some embodiments, an amount of heat transferred to the componentsfrom the first portion is greater than an amount of heat transferred tothe components from the second portion.

In some embodiments, the first portion and the second portion are joinedat a transition such that the first resistance transitions to the secondresistance at the transition.

In some embodiments, the first portion has a first cross-sectional area;and, the second portion has a second cross-sectional area that isgreater than the first cross-sectional area.

In some embodiments, the cross-sectional area of at least one of thefirst portion or the second portion varies along its length.

In some embodiments, a cross-sectional area of the heating elementtransitions from the first cross-sectional area to the secondcross-sectional area at the transition.

In some embodiments, the first portion and the second portion have anequal width; the first portion has a first thickness; and, the secondportion has a second thickness that is greater than the first thickness.

In some embodiments, the first portion has a first curvature and thesecond portion has a second curvature that is different than the firstcurvature. Optionally, the first curvature transitions to the secondcurvature at the transition. In some embodiments, the first portion iscurved and the second portion is straight.

In some embodiments, the resistive material is conforms to the shape ofthe components.

In some embodiments, the first portion is configured to conform to afirst shape of at least one of the components and the second portion isconforms to a shape that is different from the first shape. Optionally,the ratio of the first thickness to the second thickness is 0.012:0.015.Optionally, the width is 0.25 inches, the first thickness is 0.012inches, and the second thickness is 0.015 inches.

In some embodiments, the heating element is made from a homogeneousresistive material.

In some embodiments, the heating element is made using an electricaldischarge machining process.

In some embodiments, the heating element is made using a processselected from the group of milling, laser beam machining, abrasive jetmachining, electrochemical machining, electron beam machining, water jetmachining, and 3D printing.

In some embodiments, the heating element is made without bending theresistive material.

Other objectives are achieved by providing A method of fusing materials;comprising the steps of: providing a holder configured to position atleast two components together for fusing; providing a heating elementconfigured to apply heat to the at least two components to form a seal;positioning the at least two components using the holder; and, applyingan electrical current to the heating element; wherein the heatingelement has a first end and a second end, and comprises a resistivematerial; a first portion of the heating element exhibits a firstelectrical resistance; a second portion of the heating element exhibitsa second electrical resistance; and, the first portion and the secondportion generate different heat levels.

In some embodiments, the amount of heat transferred to the componentsfrom the first portion is greater than an amount of heat transferred tothe components from the second portion.

In some embodiments, the first portion and the second portion are joinedat a transition such that the first resistance transitions to the secondresistance at the transition.

In some embodiments, the first portion has a first cross-sectional area;and, the second portion has a second cross-sectional area that isgreater than the first cross-sectional area.

In some embodiments, the cross-sectional area of at least one of thefirst portion or the second portion varies along its length.

In some embodiments, the cross-sectional area of the heating elementtransitions from the first cross-sectional area to the secondcross-sectional area at the transition.

In some embodiments, the first portion and the second portion have anequal width; the first portion has a first thickness; and, the secondportion has a second thickness that is greater than the first thickness.

In some embodiments, the first portion has a first curvature and thesecond portion has a second curvature that is different than the firstcurvature. Optionally, the first curvature transitions to the secondcurvature at the transition.

In some embodiments, the first portion is curved and the second portionis straight.

In some embodiments, the resistive material is configured to conform tothe shape of the components.

In some embodiments, the first portion is conforms to a first shape ofat least one of the components and the second portion conforms to ashape that is different from the first shape. Optionally, the ratio ofthe first thickness to the second thickness is 0.012:0.015. Optionally,the width is 0.25 inches, the first thickness is 0.012 inches, and thesecond thickness is 0.015 inches.

In some embodiments, the heating element is made from a homogeneousresistive material.

Other objects of the invention and its particular features andadvantages will become more apparent from consideration of the followingdrawings and accompanying detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a medical IV bag formed by fusingthermoplastic materials.

FIG. 2 is a perspective view of a known heat resistive sealing elementfor fusing the medical IV bag shown in FIG. 1.

FIG. 3 is a perspective view of a heat resistive sealing elementaccording to aspects of the invention for fusing the medical IV bagshown in FIG. 1.

FIG. 4 is a top view of the sealing element shown in FIG. 3.

FIG. 5 is a side view showing a profile of the sealing element shown inFIG. 3.

FIG. 6 is a side detail view of the sealing element shown in FIG. 5.

FIG. 7 is another side detail view of the sealing element shown in FIG.5.

FIG. 8 is another perspective view of the sealing element shown in FIG.3.

FIG. 9 is another side view of the sealing element shown in FIG. 3.

FIG. 10 is a flow chart illustrating a method of creating a sealingelement according to aspects of the invention.

FIG. 11 is a flow chart illustrating a method of creating a heat sealingdevice according to aspects of the invention.

FIG. 12 is a flow chart illustrating a method of creating a seal byfusing parts according to aspects of the invention.

FIG. 13 is a perspective view of a portion of an inflatable cushionformed by fusing thermoplastic materials according to aspects of theinvention.

FIG. 14 is a perspective view of another heat resistive sealing elementaccording to aspects of the invention for fusing the cushion shown inFIG. 13 according to aspects of the invention.

FIG. 15 is a side view showing a profile of the sealing element shown inFIG. 14.

FIG. 16 is a side detail view of the sealing element shown in FIG. 15.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates a portion of a thermoplastic medical IV bag 100 madefrom thermoplastic sheets 110 and 120, and having tubular ports 130 and140. Bag 100 is made by fusing ports 130 and 140 between sheets 110 and120 by forming a heat seal 150. Heat seal 150 has sections 160, 170,180, 190, and 195. Those having skill in the art will appreciate thatthis application is not limited to use as an IV bag, and in fact manyother uses and applications are possible without departing from theinvention.

Heat seal 150 fuses sheets 110 and 120 directly to one another insections 160, 170, and 180. In sections 190 and 195, heat seal 150 fusessheets 110 and 120 to tubes 130 and 140.

Bag 100 is an example of a typical tube to bag seal construction foundin many medical devices, for example. In such arrangements, a simple bagmade from two film layers, along with two tubes that act as ports, areprovided. The two film layers are arranged with the tubes disposedtherebetween, and then peripheries of the film layers are sealed to oneanother, with the peripheries of the film layers also being sealed tothe two tubes to create a fluid-tight pouch having two ports.

FIG. 2 illustrates components of a known impulse heat sealing apparatusfor creating a seal 150 as described regarding FIG. 1.

To create seal 150, heating elements 200 and 200′ are first positionedwith respect to bag 100 using a suitable mechanism (not shown), holdingtubes 130 and 140 between sheets 110 and 120 by applying pressure in thedirection indicated by arrows 250. Various holding mechanisms are knownin the art, including but not limited to clamps, presses, jaws,fixtures, tooling, platens, bars and the like, and those having ordinaryskill in the art will appreciate that any of these can be used withoutdeparting from the invention. Heat is applied to bag 100 by passing anelectric current through elements 200 and 200′.

Heating elements 200 and 200′ are shaped to accommodate the contours oftubes 130 and 140, and are made by bending a straight ribbon ofresistance material with a constant cross-sectional area into shape,according to known methods. The uniform cross-sectional area of theheating elements results in a uniform temperature along each elementduring sealing. This is due to the constant current density that arisesalong the length of the elements when current is applied during sealing.

The desire is to seal tubes 130 and 140 into the edge seal 150 of thebag 100, but due to the different mass of the film versus the tubes,higher temperatures are required in the specific areas of interface 190,195 between the film layers and the tubes, as compared to thetemperatures required in the areas 160, 170, 180 where the film layersare directly sealed to one another.

Accordingly, in order to fuse tubes 130 and 140 between sheets 110 and120, the temperature of heating elements 200 and 200′ must be greaterthan would be required to fuse sheets 110 and 120 together. This isbecause the greater mass of tubes 130 and 140 requires additional heatto melt, and also acts as a heat sink.

However, the higher temperatures required to fuse tubes 130 and 140between sheets 110 and 120 may undesirably deform bag 100, for instance,by producing shrinkage 280 (FIG. 1) in seal 150 due to overheating ofthe materials. This shrinkage can result in damage or undesirablepuckering 285 (FIG. 1) of bag 100.

Furthermore, bending heating elements 200, 200′ to shape can distort orthin the heating elements 200, 200′ locally, producing a locallydecreased cross-sectional area and increased temperatures due to theincreased current density at the bends. This can also result inincreased heating and damage.

Conversely, the bending may not be adequate to create a sharp transitionbetween the portions of the elements 200, 200′ corresponding to straightsections 160, 170, 180 and curved sections 190, 195, resulting ininadequate contact between elements 200, 200′ and seal 150. Thisinadequate contact can result in reduced heat transfer to seal 150, andcan weaken the seal.

FIG. 3 illustrates an example resistive heat sealing element 300according to aspects of the invention.

Sealing element 300 may be made from nichrome or any other suitableresistive heating material known in the art. When a sufficient currentis passed through sealing element 300, its temperature will rise inaccordance with its material and structural properties.

Sealing element 300 includes straight portions 310, 320, and 330, curvedportions 340 and 350, as well as end portions 360 and 370. End portions360 and 370 are shown featuring mounting holes, but these may be omittedor supplemented in some implementations without departing from theinvention. Sealing element 300 has a uniform width 400, although in someimplementations the width may vary. Although example sealing element 300is shown as having a linear shape, those having skill in the art willappreciate that a sealing element may have a serpentine, looped, orcircular “donut” shape, such as for producing curved, circular, or othernon-linear seals, without departing from the invention.

FIGS. 4 and 5 are alternate views of the sealing element 300 shown inFIG. 3. Unlike known sealing elements 200 and 200′ (FIG. 2), sealingelement 300 has different thicknesses at different locations along itslength. For example, end portions 360 and 370 each have a thickness 610;straight portions 310, 320, and 330 each have a thickness 620; andcurved portions 340 and 350 each have a thickness 630.

Thickness 610 is greater than thickness 620, and thickness 620 isgreater than thickness 630. In this example, the difference inthicknesses of sealing element 300 results in a corresponding differencein cross-sectional areas. This means that when a current is passedthrough sealing element 300, thinner sections will exhibit increasedheating due to the increased current density in those regions. Here, theend portions 360 and 370 will have the greatest cross-sectional area,and will accordingly exhibit the coolest temperatures. Curved portions340 and 350 will have the smallest cross-sectional area, and willaccordingly exhibit the highest temperatures.

In summary, it can be seen that by varying the thickness of the sealelement in desired areas, a single seal element can be used to createdesired temperatures in desired areas. More specifically, as can be seenin the drawings, the “flat areas” which are used to create thefilm-to-film seals are greater in thickness (e.g., 0.015 inches) versusthe thickness (e.g., 0.012 inches) of the “curved areas” which are usedto create the film-to-tube seals.

Varying the thickness of a heating element in this way can have theadvantage of selectively providing increased heating to areas of highermass and decreased heating to portions of element 300 that are not usedfor sealing, saving energy costs.

FIG. 6 shows detail view A of the sealing element 300 as shown in FIG.5, illustrating a clearly defined abrupt transition 600 between endportion 360 and straight portion 310.

FIG. 7 shows detail view B of the sealing element 300 as shown in FIG.5, illustrating a clearly defined abrupt transition 700 between straightportion 310 and curved portion 340.

According to some aspects of the invention, providing clearly definedabrupt transitions 600, 700 can have the advantage of allowing improvedcontrol of heat delivery to different portions of the seal duringsealing. Such sharp transitions are possible by machining rather thanbending heating element 300, as further discussed herein.

It should be noted that in some applications according to the invention,certain transitions (such as transition 600) may not be required to besharply defined and abrupt. For example, in applications where theapplication of heat to the seal 150 begins in straight portion 310 anddoes not overlap transition 600, a sharp drop in temperature, andaccordingly thickness, may not be critical.

In an example implementation, a sealing element (not shown) with asimilar profile to element 300, having a width of 0.25″, end thicknessesof 0.030″ straight section thicknesses of 0.015″ and curve thicknessesof 0.012″ was analyzed. It was found that an electrical current appliedto this sealing element (not shown) could result in a temperature rangeof over 100 degrees Fahrenheit between the straight and curved sections.It will be clear to those having skill in the art that altering thesedimensions can result in greater or lesser ranges of temperatures.

This controllability of temperature along the length of a sealingelement can have the advantage of improving seals by enabling moreprecise heat delivery to regions having different melting and/orheat-sink properties.

FIGS. 8 and 9 illustrate sealing element 300 as shown in FIGS. 3-8,wherein element 300 is shown as machined from a block of a resistiveheating element material 900, according to aspects of the invention. Insome implementations, material 900 is nichrome or stainless steel,although other suitable materials will be evident to those having skillin the art.

As discussed earlier, it is difficult to achieve sharp transitionsbetween portions of a sealing element having different shapes usingtypical methods of bending the element to shape. This is because bendingproduces strain in the material which can thin or distort the element,resulting in uneven heating which can damage the parts to be sealed.

In order to avoid this problem, heating element 300 is machined from ablock of resistive material 900 to create the desired shape,thicknesses, and abrupt transitions between areas of different thicknessand areas of different shape.

In some implementations, sealing element 300 is machined from block 900using an electrical discharge machining (EDM) process. However, othermethods of machining are possible within the scope of invention,including but not limited to milling, laser beam machining, abrasive jetmachining, electrochemical machining, electron beam machining, and waterjet machining.

Machining the sealing element in this way can have the advantage ofenabling sharp transitions to be created between regions of the sealingelement having different thicknesses and/or different shapes.

It should be noted that according to some aspects of the invention, themachining process is not necessary, so long as the profile of thesealing element includes regions having different cross-sectional areas.According to other aspects of the invention, a sealing element may bemachined from a block of resistive heating material and furtherprocessed by bending. An example of an application where a combinationof machining and bending may be appropriate would be in a circumstancewhere a sharp transition between shapes or thicknesses is required inone portion of the heating element but not in another.

FIG. 10 illustrates a method 1000 of creating a sealing elementaccording to aspects of the invention.

In step 1010, a block of resistive heating material is provided. Theblock of resistive heating material may be made from nichrome, stainlesssteel, or any other suitable resistive heating material known in theart.

In step 1020, a band of material is cut from the block of resistiveheating material such that the band has a varying profile. The band ofmaterial forms a heating element that may be configured as discussedherein according to any aspect of the invention.

FIG. 11 illustrates a method 1100 of creating a heat sealing deviceaccording to aspects of the invention.

In step 1110, a holding device is provided, which is configured to applypressure to at least two components. The holding device is configuredsuch that the components can be held in a desired position for fusing.Various holding devices are known in the art, including but not limitedto clamps, presses, jaws, fixtures, tooling, platens, bars and the like,and those having ordinary skill in the art will appreciate that any ofthese can be used without departing from the invention

In step 1120, a resistive heating element is installed into the holdingdevice and configured to heat the components when a current is appliedto the resistive heating element for a desired amount of time and thenallowed to cool. The resistive heating element may be configured asdiscussed herein according to any aspect of the invention.

FIG. 12 illustrates a method 1200 of fusing parts according to aspectsof the invention.

In step 1210, a heat sealing device is provided having a resistiveheating element which has a shape designed to correspond with thecontours of a particular arrangement of parts to be fused. The resistiveheating element may be configured as discussed herein according to anyaspect of the invention.

In step 1220, components desired to be fused are inserted into the heatsealing device.

In step 1230, electrical current is applied to the resistive heatingelement such that heat is applied to the components.

In step 1240, the current is switched off, and the components areallowed to cool.

In step 1250, the components are removed from the heat sealing device.

FIG. 13 shows another example heat sealing application where aninflatable cushion 1300 includes a molded thermoplastic port 1310 sealedbetween two monolayer films. Port 1310 interacts with the seal in asimilar fashion to the tubes shown in FIGS. 1 and 2, except thatthermoplastic port 1310 has a different shape and mass distribution.Those having skill in the art will appreciate that this application isnot limited to use as an inflatable cushion, and in fact many other usesand applications applications are possible without departing from theinvention.

FIG. 14 illustrates a sealing element 1400 having a shape adapted forthe application shown in FIG. 13. Sealing element 1400 has end portions1410 and 1420, straight portions 1430 and 1440, and as a shaped portion1450. End portions 1410 and 1420 are shown featuring mounting holes, butthese may be omitted or supplemented in some implementations withoutdeparting from the invention. Sealing element 1400 has a uniform width1460, although in some implementations the width may vary.

FIG. 15 is an alternate view of the sealing element 1400 shown in FIG.14.

Sealing element 1400 has different thicknesses at different locationsalong its length. For example, end portions 1410 and 1420 each have athickness 1510; straight portions 1430 and 1440 each have a thickness1520; and shaped portion 1450 has a thickness 1530.

Thickness 1510 is greater than thickness 1520, and thickness 1520 isgreater than thickness 1530. The variation in thicknesses of sealingelement 1400 results in a corresponding variation in cross-sectionalarea. This means that when a current is passed through sealing element1400, sections having a lesser thickness will exhibit increased heatingdue to the increased current density in those regions. Here, endportions 1410 and 1420 will have the greatest cross-sectional area, andwill accordingly exhibit the coolest temperatures. Shaped portion 1450will have the smallest cross-sectional area, and will accordinglyexhibit the highest temperatures.

Varying the thickness of a heating element in this way can have theadvantage of selectively providing increased heating to areas of highermass and decreased heating to portions of element 1400 that are not usedfor sealing, saving energy costs.

FIG. 16 shows a detail view C of the sealing element 1400 as shown inFIG. 16, illustrating the transition 1600 between end portion 1430 andstraight portion 1450.

Providing a sharp transition 1600 between thickness 1520 and thickness1530 can have the advantage of providing improved control of heatdelivery to different portions of the seal during sealing.

Port 1310 (FIG. 13) has a profile that varies continuously betweenthinner and thicker portions. Accordingly, in some implementations (notshown) the thickness of shaped portion 1450 of sealing element 1400 mayvary in a continuous fashion to correspond to the continuously varyingprofile of port 1310. This can have the added advantage of even moreprecisely controlling the application of heat to areas of a part havingheat-sink properties that vary continuously along the length of theseal.

Although the invention has been described with reference to a particulararrangement of parts, features and the like, these are not intended toexhaust all possible arrangements or features, and indeed manymodifications and variations will be ascertainable to those of skill inthe art.

What is claimed is:
 1. A method of manufacturing a heat sealing device, comprising the steps of: providing a heating element; providing an electrical power source connected to the heating element; and, providing a holder configured to position the components with respect to the heating element; wherein said heating element has a first end and a second end and comprises a resistive material; a first portion of said heating element exhibits a first electrical resistance; a second portion of said heating element exhibits a second electrical resistance; and, wherein when electrical current from said electrical power source is passed through said heating element, the first portion and the second portion generate different heat levels.
 2. The method of claim 1, wherein: an amount of heat transferred to the components from the first portion is greater than an amount of heat transferred to the components from the second portion.
 3. The method of claim 1, wherein said first portion and said second portion are joined at a transition such that the first resistance transitions to the second resistance at the transition.
 4. The method of claim 1, wherein said first portion has a first cross-sectional area; and, said second portion has a second cross-sectional area that is greater than the first cross-sectional area.
 5. The method of claim 4, wherein the cross-sectional area of at least one of said first portion or said second portion varies along its length.
 6. The method of claim 4, wherein a cross-sectional area of the heating element transitions from the first cross-sectional area to the second cross-sectional area at the transition.
 7. The method of claim 1, wherein: said first portion and said second portion have an equal width; said first portion has a first thickness; and, said second portion has a second thickness that is greater than said first thickness.
 8. The method of claim 1, wherein said first portion has a first curvature and said second portion has a second curvature that is different than the first curvature.
 9. The method of claim 8, wherein the first curvature transitions to the second curvature at the transition.
 10. The method of claim 1, wherein said first portion is curved and said second portion is straight.
 11. The method of claim 1, wherein said resistive material is conforms to the shape of the components.
 12. The method of claim 1, wherein said first portion is configured to conform to a first shape of at least one of the components and said second portion is conforms to a shape that is different from the first shape.
 13. The method of claim 7, wherein the ratio of the first thickness to the second thickness is 0.012:0.015.
 14. The method of claim 7, wherein the width is 0.25 inches, the first thickness is 0.012 inches, and the second thickness is 0.015 inches.
 15. The method of claim 1, wherein said heating element is made from a homogeneous resistive material.
 16. The method of claim 1, wherein the heating element is made using an electrical discharge machining process.
 17. The method of claim 1, wherein the heating element is made using a process selected from the group of milling, laser beam machining, abrasive jet machining, electrochemical machining, electron beam machining, water jet machining, sintered molding, and 3D printing.
 18. The method of claim 1, wherein the heating element is made without bending the resistive material.
 19. The method of claim 1, wherein a first resistive coating is applied to a first area on the element.
 20. The method of claim 19, wherein a second resistive coating exhibiting a resistance different from the first resistive coating is applied to a second area on the element.
 21. A method of fusing materials; comprising the steps of: providing a holder configured to position at least two components together for fusing; providing a heating element configured to apply heat to the at least two components to form a seal; positioning the at least two components using the holder; and, applying an electrical current to the heating element; wherein said heating element has a first end and a second end, and comprises a resistive material; a first portion of said heating element exhibits a first electrical resistance; a second portion of said heating element exhibits a second electrical resistance; and, the first portion and the second portion generate different heat levels.
 22. The method of claim 21, wherein an amount of heat transferred to the components from the first portion is greater than an amount of heat transferred to the components from the second portion.
 23. The method of claim 21, wherein said first portion and said second portion are joined at a transition such that the first resistance transitions to the second resistance at the transition.
 24. The method of claim 21, wherein said first portion has a first cross-sectional area; and, said second portion has a second cross-sectional area that is greater than the first cross-sectional area.
 25. The method of claim 24, wherein the cross-sectional area of at least one of said first portion or said second portion varies along its length.
 26. The method of claim 24, wherein a cross-sectional area of the heating element transitions from the first cross-sectional area to the second cross-sectional area at the transition.
 27. The method of claim 21, wherein: said first portion and said second portion have an equal width; said first portion has a first thickness; and, said second portion has a second thickness that is greater than said first thickness.
 28. The method of claim 21, wherein said first portion has a first curvature and said second portion has a second curvature that is different than the first curvature.
 29. The method of claim 28, wherein the first curvature transitions to the second curvature at the transition.
 30. The method of claim 28, wherein said first portion is curved and said second portion is straight.
 31. The method of claim 21, wherein said resistive material is configured to conform to the shape of the components.
 32. The method of claim 21, wherein said first portion is conforms to a first shape of at least one of the components and said second portion conforms to a shape that is different from the first shape.
 33. The method of claim 27, wherein the ratio of the first thickness to the second thickness is 0.012:0.015.
 34. The method of claim 27, wherein the width is 0.25 inches, the first thickness is 0.012 inches, and the second thickness is 0.015 inches.
 35. The method of claim 21, wherein said heating element is made from a homogeneous resistive material.
 36. The method of claim 21, wherein a first resistive coating is applied to a first area on the element.
 37. The method of claim 36, wherein a second resistive coating exhibiting a resistance different from the first resistive coating is applied to a second area on the element.
 38. The method of claim 21, wherein the heating element is configured to cut at least one of the components while forming a seal.
 39. The method of claim 38, wherein the heating element cuts the at least one of the components using heat.
 40. The method of claim 21, wherein the at least two components comprise at least two folds of one object.
 41. The method of claim 40, wherein the object is a thermoplastic film that has been folded to form a gusset. 